In many aircraft actuation systems it is desirable to limit the amount of torque the actuators are capable of exerting. In modern aircraft systems, high speed air or hydraulic motors are used to drive flaps, landing gear doors, and other power-operated accessories to minimize weight. Torque limiters are used in the event that the flap, door or the like becomes jammed for any reason. However, because of high rotational inertia, the prime moving means or motors can provide an output torque considerably greater than their normal output if a jam occurs in the driven mechanism. Therefore, in order to prevent damage to the driven mechanism in the event of jamming, torque limiting devices are used to limit the output of the power means.
Many torque limiting devices perform the torque limiting function by a ball ramp torque limiter that abruptly brings the system to a halt in the event the torque through the device exceeds a predetermined value. It is desirable to put the torque limiter on as high speed (and low torque) a shaft as possible to keep component sizes to a minimum. Unfortunately, with a high speed torque limiter, torque spikes due to sudden stoppage can become quite large. Therefore, some type of shock absorbing device, such as a rubber torsion member, is required on the grounding member of the device to reduce the torque spike.
Some actuation systems also find it necessary to isolate the motor inertia, as by the use of a slip clutch, from the torque limiter to further reduce loading of the components and minimize weight. It would be advantageous to eliminate the need for a rubber torsion member and a slip clutch, reducing weight and complexity while increasing reliability of the system. Thrust bearings typically utilized with ball ramp torque limiters also add weight and should advantageously be eliminated if possible.
Examples of torque limiting devices, such as for use in aircraft flight controls with flap systems or the like, are shown in U.S. Pat. Nos. 3,596,740 to Nau, dated Aug. 3, 1971, and 4,030,578 to Cacciola et al, dated June 21, 1977. Both of these patents show types of torque limiters which generally are related to the general problems described above. However, the devices are rather complex and do not sufficiently reduce the weight of the systems.
This invention is directed to solving the above problems and satisfying a need for a new and improved, simple, cost effective and low weight torque limiter of the character described.